Infection of the body by bacteria

Why do bacteria invade the body?

The main reason why bacteria invade the bodies of human beings and other animals is because those bodies harbour environments where the bacteria can survive and multiply. Body fluids, such as plasma, are rich in sugars, vitamins, minerals and other chemicals which bacteria can use as nutrients.

How do bacteria get into the body?

In order to get into the body, bacteria must come into direct physical contact with it. This can happen in many different ways. An individual may acquire bacteria in any of the following ways.

By direct contact with a person who is infected with that bacterium. A common example of this method of infection is Meningitis, which is caused by the bacterium Neisseria Meningitidis.

Through dust or liquid droplets in the air. Tuberculosis, caused by the bacterium Mycobacterium tuberculosis, can be contracted in this way, by coming into contact with sputum expectorated (coughed-up) by a person infected by Mycobacterium tuberculosis.

By consuming contaminated food or water. Many infections happen this way, such as Salmonella, Cholera and Typhoid.

By puncture wounds, such as animal or inset bites. Examples include the Rabies virus, which can be contracted through a bite from an infected animal, and Malaria, which can be contracted through a bite from a mosquito that carries the malaria virus.

Although these are the main methods by which bacteria enter the body, there are also many other methods.

What does the body do to protect itself?

The human body protects itself from infection in many different ways. The first lines of defence are known as barrier defences. The main points of entry into the body are the skin, the eyes, the respiratory tract and the gastrointestinal tract.

The skin protects itself by exuding secretions from the sweat and sebaceous glands, which contain fatty acids that inhibit the growth of bacteria. Also, the skin is constantly renewing itself, by allowing the top layers of cells to die and be replaced by newer cells from underneath.

The stomach protects itself by containing a strong acid, in which it is very difficult for bacteria to survive.

The intestines are protected by the fact there is already a large population of bacteria living there, which means that any invading bacteria has to compete with the existing bacteria to find a niche for itself. The existing bacteria, known as the normal flora, occupy most of the available niches, produce anti-biotic chemicals which inhibit invaders, and may also outcompete invaders for the available food supply.

If the invading organism manages to bypass all of these defenses, the immune system then swings into action.